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RATIONALE: Drugs used in chemotherapy, such as gemcitabine hydrochloride and genistein, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Giving gemcitabine hydrochloride together with genistein may kill more tumor cells.

PURPOSE: This phase II trial is studying how well giving gemcitabine hydrochloride together with genistein works in treating women with stage IV breast cancer.

Determine the duration of response and survival of patients treated with this regimen.

Determine the time to disease progression in patients treated with this regimen.

Determine the quantitative and qualitative toxic effects of this regimen in these patients.

Correlate plasma genistein levels with response in patients treated with this regimen.

OUTLINE: Patients receive oral genistein once daily on days -7 to 1. Patients also receive gemcitabine hydrochloride IV on days 1 and 8 and oral genistein once daily on days 1-21. Courses repeat every 21 days in the absence of disease progression or unacceptable toxicity.

PROJECTED ACCRUAL: A total of 36 patients will be accrued for this study.

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Ages Eligible for Study:

18 Years to 120 Years (Adult, Senior)

Sexes Eligible for Study:

Female

Accepts Healthy Volunteers:

No

Criteria

DISEASE CHARACTERISTICS:

Histologically or cytologically confirmed breast cancer

Stage IV disease

Clinical and/or radiological evidence of metastatic disease

Measurable disease

Prior radiotherapy allowed provided there is ≥ 1 measurable disease site outside the radiation field

No concurrent nutritional supplements, herbal agents, or high doses of antioxidants (e.g., vitamins C, D, or E) that may interact with, antagonize, alter, or imitate the potential effects of gemcitabine hydrochloride or genistein